Due to their excellence in thermal moldability and low production cost, hoses mainly formed with polyvinyl chloride resins (PVC) have generally been employed as electric cleaner hoses. For example, hoses composed of a hose wall and a wire reinforcement covered with a resin and united with the hose wall are known. A hose like these can be fabricated by spirally winding a resin-covered wire reinforcement, which is a steel wire covered with a PVC resin, around a mandrel, further covering the resin-covered reinforcement with a tube of a soft PVC resin or spirally winding a tape of a soft PVC resin around the resin-covered reinforcement to form a hose wall, separating the hose thus formed from the mandrel. In the hose thus obtained, the hose wall and the resin-covered reinforcement are bonded together or fused such as to be unitary with each other.
However, for making soft PVC resins flexible, a variety of liquid plasticizers are added thereto . When hoses fabricated with such soft PVC resins are used over long periods of time, the plasticizers contained therein begin to bleed out (seep out) on their surfaces. As a result, the plasticizer content of the PVC is lowered with an increase in hardness (stiffness). Consequently, these hoses become less flexible and their risk of fatigue failure becomes higher as the hoses are bent repeatedly.
In addition, with such recent global environmental problems as poisonous gases generated by burning PVC waste leading to an acid rain as well as the PVC itself being considered carcinogenic, there is a trend toward imposing restrictions on the use of PVC resins. Moreover, hoses made with PVC resins are rather heavy and difficult to handle.
U.S. Pat. No. 6,024,134 discloses a hose which comprises a hose wall formed by spirally winding a laminated tape and bonding the adjacent side edges of the covering layer each other, and a hard spiral reinforcement for reinforcing the hose wall and retaining the hose configuration, wherein the laminated tape is constituted of a main layer of a polyester-series thermoplastic resin polyurethane resin and a covering layer of a soft resin is laminated on at least one surface of the main layer. This literature describes that this hose is excellent in flexibility and durability, the degree of its shrinkage is low, and that it can favorably be used as a duct hose.